1. Field of the Invention
The present invention generally relates to positioning systems. More particularly, the present invention relates to a positioning system used for a combiner minor of a head-up display system.
2. Description of Related Art
A head-up display or HUD is a transparent display that presents data without requiring users to look away from their usual viewpoints. Although they were developed for just military aviation in the earlier time, it is becoming common that using HUDs in commercial aircraft, automobiles and other applications. A typical HUD contains three primary components: a combiner, a projector unit and a video generation computer. The combiner is a semi-transparent mirror that is positioned in front of the pilot/driver to display the virtual picture with the required information, i.e., a pilot/driver can see the view in front of the aircraft/vehicle through the combiner of the HUD. Combiners can be concave or flat, and usually have a special coating that reflects the monochromatic light projected onto it from the projector unit while allowing all other wavelengths of light to pass through. On some aircrafts, the combiners are easily removable or can be rotated out of the way by aircrew. The projection unit projects the image onto the combiner for the user to view. Projection units can be either below or above the combiners. The computer provides the required information/data to be displayed.
Some mechanisms of combiner positioning for a HUD have already been known in the art. A retractable combiner is disclosed in US patent Pub. No. 2008/0285138 A1. In such kinematic mechanisms, the combiner is stored in a protected housing when it is in a parking position. The combiner is mounted on a movable supporting frame which is displaceable between the parking position and an operating position. The combiner is retracted back into the housing in the parking position and extended to the external of the housing in the operating position.
Another combiner positioning mechanism is proposed in US patent Pub. No. 2009/0086329 A1. In the combiner positioning system of this article, the system is arranged on a frame including a base plate. A movable carrier is provided for supporting the combiner within the frame and it is movable between the parking position where the combiner is in a retracted position and the operating position where the combiner is in a fully extended position. The movable carrier is driven by a screw spindle coupled to a stepping motor. The movement is guided by side walls with cams and teeth to drive a synchronous movement. It includes the possibility for angular fine adjustment of combiner position when the combiner is in the operating position.
Still, the required space for such a kinematic mechanism of combiner positioning system including many parts for accurate movement limits the possibilities for reduced outline of the HUD. The design does not offer the wished flexibility to follow requirements for dashboard and different windshields from car makers. Additionally, the two major functions, combiner movement and combiner adjustment are strongly linked with each other. Therefore, the maximum speed of combiner movement cannot be increased without compromising the resolution of combiner adjustment.
Thus, capability of fine adjustment is also very important for the kinematic mechanisms of combiner positioning. Sometimes, the virtual images displayed on the combiner cannot be read with the same ease when the position of the combiner s not in a best condition. The small distances between the user of a vehicle and the combiner and size differences between the vehicle users may bring about the requirement of accuracy of the combiner positioning system.